/*
 * Copyright 2011 The Apache Software Foundation
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.hbase.coprocessor;

import org.apache.hadoop.hbase.CoprocessorEnvironment;

/**
 * Carries the execution state for a given invocation of an Observer coprocessor
 * ({@link RegionObserver}, {@link MasterObserver}, or {@link WALObserver})
 * method.  The same ObserverContext instance is passed sequentially to all loaded
 * coprocessors for a given Observer method trigger, with the
 * <code>CoprocessorEnvironment</code> reference swapped out for each
 * coprocessor.
 * @param <E> The {@link CoprocessorEnvironment} subclass applicable to the
 *     revelant Observer interface.
 */
public class ObserverContext<E extends CoprocessorEnvironment> {
	private E env;
	private boolean bypass;
	private boolean complete;

	public ObserverContext() {
	}

	public E getEnvironment() {
		return env;
	}

	public void prepare(E env) {
		this.env = env;
	}

	/**
	 * Call to indicate that the current coprocessor's return value should be
	 * used in place of the normal HBase obtained value.
	 */
	public void bypass() {
		bypass = true;
	}

	/**
	 * Call to indicate that additional coprocessors further down the execution
	 * chain do not need to be invoked.  Implies that this coprocessor's response
	 * is definitive.
	 */
	public void complete() {
		complete = true;
	}

	/**
	 * For use by the coprocessor framework.
	 * @return <code>true</code> if {@link ObserverContext#bypass()}
	 *     was called by one of the loaded coprocessors, <code>false</code> otherwise.
	 */
	public boolean shouldBypass() {
		boolean current = bypass;
		bypass = false;
		return current;
	}

	/**
	 * For use by the coprocessor framework.
	 * @return <code>true</code> if {@link ObserverContext#complete()}
	 *     was called by one of the loaded coprocessors, <code>false</code> otherwise.
	 */
	public boolean shouldComplete() {
		boolean current = complete;
		complete = false;
		return current;
	}

	/**
	 * Instantiates a new ObserverContext instance if the passed reference is
	 * <code>null</code> and sets the environment in the new or existing instance.
	 * This allows deferring the instantiation of a ObserverContext until it is
	 * actually needed.
	 *
	 * @param env The coprocessor environment to set
	 * @param context An existing ObserverContext instance to use, or <code>null</code>
	 *     to create a new instance
	 * @param <T> The environment type for the context
	 * @return An instance of <code>ObserverContext</code> with the environment set
	 */
	public static <T extends CoprocessorEnvironment> ObserverContext<T> createAndPrepare(T env, ObserverContext<T> context) {
		if (context == null) {
			context = new ObserverContext<T>();
		}
		context.prepare(env);
		return context;
	}
}
